Documents show Trayvon Martin was shot through the heart and George Zimmerman suffered broken nose

Trayvon Martin was shot through the heart at close range and George Zimmerman had a broken nose, bruises and cuts on the back of his head, new documents show.

Details revealed in nearly 200 pages of documents, photos and audio recordings also show the lead investigator in the case wanted to charge Zimmerman with manslaughter in the weeks after the 17-year-old's shooting but was overruled.

The case of Martin's shooting by Zimmerman, 28, in a gated community in Orlando, Florida, has riveted the US.

It has become a national flashpoint because the Martin family and supporters say Zimmerman singled Martin out because he was black.

The new evidence supports neighbourhood watch volunteer Zimmerman's contention that he was being beaten up on 26 February when he fired the fatal shot.

It also bolsters the argument of Martin's parents that Zimmerman was profiling Martin - visiting from Miami - and the confrontation could have been avoided.

Many of the pertinent questions remain unclear: What was in Zimmerman's mind when he began to follow Martin? How did the confrontation begin? Whose screams for help were captured on emergency service calls? And why did Zimmerman feel that deadly force was warranted?

At a hearing later this year Zimmerman is expected to claim the shooting was justified under Florida's "stand your ground" law. His lawyer, Mark O'Mara, did not return a phone call seeking comment today.

The evidence supporting Zimmerman's defence includes a photo showing him with a bloody nose on the night in question. A paramedic's report says Zimmerman had an inch-long laceration on his head and forehead abrasions.

"Bleeding tenderness to his nose, and a small laceration to the back of his head. All injuries have minor bleeding," paramedic Michael Brandy wrote.

Whether Zimmerman was injured in the altercation with Martin has been a key question. He has claimed self-defence and said he only fired because the unarmed teenager attacked him.

Zimmerman was not arrested for weeks because he invoked the law, which does not require a person to retreat in the face of a serious threat.

He was released on bail and is in hiding while he awaits trial on a second-degree murder charge. He has pleaded not guilty.

The investigator who called for Zimmerman's arrest, Christopher Serino, told prosecutors the fight could have been avoided if Zimmerman had remained in his vehicle and waited for law enforcement.

He said Zimmerman could have identified himself to Martin as a concerned citizen and talked to him instead of confronting him. The report was written on 13 March, nearly a month before Zimmerman's eventual arrest.

He said there is no evidence Martin was involved in any criminal activity as he walked from a convenience store to the home of his father's fiancee in the same gated community where Zimmerman lived.

Ben Crump, the lawyer acting for Martin's parents, said: "The police concluded that none of this would have happened if George Zimmerman hadn't gotten out of his car. If George Zimmerman hadn't gotten out of his car, they say it was completely avoidable. That is the headline."

The release of evidence did little to clear up whose voice can be heard screaming for help in the background of several emergency services calls.

Since first hearing the calls in early March, Martin's mother, Sybrina Fulton, has been unequivocal in saying that it was her son's voice on the tapes.

But Serino wrote in a report that he played an emergency services call for Martin's father, Tracy, in which the screams are heard multiple times.

"I asked Mr Martin if the voice calling for help was that of his son," the officer wrote. "Mr. Martin, clearly emotionally impacted by the recording, quietly responded 'no'."

Zimmerman's father also told investigators that it was his son yelling for help.

"That is absolutely positively George Zimmerman," Robert Zimmerman said. "He was not just yelling, he sounded like he was screaming for his life."

Investigators sent all the recordings to the FBI for analysis. They were asked to determine who was screaming and whether Zimmerman might have used an expletive in describing Martin.

But the analyst found the sound quality is too poor to decipher what Zimmerman said, nor could they say whose voice is heard "due to extreme stress and unsuitable audio quality".

The trajectory of the bullet - straight through Martin's body - does not shed light on whether Zimmerman and Martin were standing or on the ground, said Larry Kobilinsky, a professor of forensic science at John Jay College of Criminal Justice in New York.

Kobilinsky added he thought the evidence diminished prosecutors' case for second-degree murder.

AP